1. Field of the Invention
The present invention relates to a radiation imaging apparatus, a radiation imaging system, and a correction method of an image, and in particular, it is suitable for use to correct the data of an image.
2. Description of the Related Art
In recent years, demand for digitalization of X-ray images radiographed in hospitals has been on the increase. Hence, in place of the X-ray imaging apparatus that performs radiographing based on a film, a flat digital X-ray imaging apparatus (flat panel detector: hereinafter referred to as FPD) has began to be used. The FPD is an apparatus that converts radiation into an electrical signal based on a plurality of radiation detecting elements disposed in a two-dimensional array pattern. The radiation detecting element mainly uses a non-monocrystalline semiconductor such as amorphous silicon (hereunder referred to as a-Si) capable of being formed into a large area detector. Such an FPD has a sensor unit including a plurality of pixels each having a photoelectric conversion element and an indirect radiation imaging apparatus having a wavelength conversion element such as a phosphor that converts the X-rays into light of a waveband perceptible by the photoelectric conversion elements. Further, there exits also a direct type radiation imaging apparatus having a sensor unit including a plurality of elements that directly convert the X-rays into an electrical signal.
The material a-Si can be fabricated into a thin glass below 1 mm in thickness. Hence, a-Si has the advantage of being able to make thickness extremely thin as a sensor. Moreover, the FPD using a-Si as the radiation detecting element is different from an X-ray imaging apparatus that performs radiographing based on a film, and can radiograph both still images and moving images using just one apparatus. Such an FPD which is used for radiographing both still images and moving images has already been put to practical use. From now on, the FPD is expected to take the place of the apparatus such as an image intensifier (hereinafter referred to as I.I.) and the like currently used as a moving image radiographing system.
In such an X-ray imaging apparatus, before irradiating the X-rays on the photoelectric conversion elements, there is an operation that irradiates light on the device in advance. Each photoelectric conversion element generates a charge that does not depend on the incidence of X-rays thereon, in addition to the charge generated by the incident X-rays. Hereinafter, an output of the charge generated independent of the incidence of X-rays is referred to as a dark signal. Further, according to the past history of the incident X-ray irradiation, a charge is generated with a delay from the photoelectric conversion element. Hereinafter, the output of such a charge generated with a delay is referred to as an image lag. These dark signals and image lags often produce a feeling of strangeness in viewing the output image, as they appear in the image as noise.
Hence, to inhibit the effect of such dark signals and image lag, there is an FPD disclosed in U.S. Pat. No. 5,905,772. In U.S. Pat. No. 5,905,772, there is disclosed a digital X-ray imaging apparatus including a bias radiation source (electromagnetic radiation source) that radiates on a semiconductor device by electromagnetic radiation. Before radiographing an object, the generation of the dark signals, the image lag, and the like is inhibited by irradiating a light on the photoelectric conversion elements. Here, the operation to irradiate light (electromagnetic irradiation) in advance is referred to as a light reset.